BP in Space

When we go to meetings, we have to make
decisions about what stories to cover. With hundreds or even thousands of
abstracts to choose from, we have to choose the studies most likely to matter
to clinicians.

Sometimes, stories that are interesting
but perhaps not entirely relevant to a practicing clinician fall by the wayside
simply because there isn’t enough time to write them.

One such story that didn’t make the cut
from the American Society of Hypertension meeting in May was a look at blood
pressure changes in astronauts who spent three to six months on the
International Space Station.

Peter Norsk, MD, who was at the
University of Copenhagen when he performed the study but now works for NASA,
said that it was known that blood pressure is unchanged or slightly reduced
during the first two weeks of spaceflight, but that there was uncertainty about
what happens with longer flights.

To find out, he and his colleagues measured 24-hour ambulatory blood pressure
in six male astronauts before they went to space, during spaceflight, and after
they returned.

The researchers found that systolic
blood pressure decreased by about 10 mm Hg during spaceflight (from an average
of about 103 mm Hg on Earth). It
increased to baseline levels about two months after the astronauts returned
home.

Also during spaceflight, cardiac output
increased and diastolic blood pressure and systemic vascular resistance
decreased. Those also returned to normal back on Earth.

The conclusion, Norsk said, is that
gravity is increasing blood pressure, decreasing cardiac output, and
restricting the small arteries here on Earth.

So considering the fact that only 525
people have been to space, according to Norsk, what do these findings mean for
the rest of us?

They have "some implications for
understanding whether gravity could play a role in developing
hypertension," he said at a press briefing.

"I am not claiming everybody
should go to space,” Norsk said with tongue firmly in cheek. “I'm doing this
research to understand the effect of everyday load of gravity on our normal
physiology.”

But, he added, the primary goal of
NASA’s research is to safeguard astronauts, and this information on blood
pressure and cardiac output will be one part of the entire risk profile to be
considered as longer spaceflights – including those to Mars – are planned.

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